<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <!-- 根据表达式的真假 切换元素display css属性 -->
        <!-- 假值： '' undefined NAN null 0 flase-->
        <h3 v-model="">{{msg}}</h3>
    </div>
    <script src="https://cdn.bootcdn.net/ajax/libs/vue/2.6.12/vue.js"></script>
    <script>
        var vm = new Vue({
            el:'#app',
            data:{
                msg:'修饰符',
                flag:false
            }
        });
    </script>
</body>
</html>